Cell-to-cell communication is a fundamental process in cell biology that is necessary for proper development and tissue homeostasis. When deregulated, it can also lead to developmental abnormalities and human diseases, such as cancer. In recent years, microvesicles (MVs) have emerged as a novel form of cell-to-cell communication that is frequently used by cancer cells to promote the malignant state. Specifically, MVs are small (0.1-2 ?m) vesicular structures that are derived directly from cell plasma membranes and are shed into the cells' surrounding environment. MVs have the ability to fuse to other cells and transfer cargo such as signaling proteins, mRNAs, and miRNAs. The sharing of cancer cell- derived MV cargo with normal cells has been shown to induce the transformation of the normal cells, and this raised the possibility that other cell types, such as embryonic stem (ES) cells and differentiated cells, might also generate MVs and use them to alter the behavior of neighboring cells. Indeed, feeder layer- independent mouse ES cells and differentiated cells derived from these ES cells generate and shed MVs, and a mass spectrometry analysis of ES cell-derived MVs revealed that they contain many proteins, including cytoskeletal components and transcription factors. Preliminary findings suggest that ES cell MVs, when isolated and then added to cultures of serum-starved NIH3T3 fibroblasts, can promote the survival of fibroblasts, while MVs derived from differentiated cells may be able to enhance the differentiation of ES cells into specific cell lineages. The primary focus of this investigation is to better understand this novel form of cellular communication by determining how specific cargo is trafficked into the MVs and to elucidate the biological effects and mechanisms of both ES cell and differentiated cell MVs on cell growth, survival, and differentiation. To this end, the following lines of investigation will be carried out: 1) Determin the biological actions of ES cell- and differentiated cell-derived MVs on the growth and survival of ES cells and normal cells. In addition, the effects of both types of MVs on the differentiation f ES cells will be examined. 2) Determine the mechanism behind the biological effects of the MVs derived from ES cells and differentiated cells. In this aim, emphasis will be placed on identifying the protein component(s) of the MVs that promote the survival of other cells. 3) Determine the methods by which proteins are trafficked into the MVs of ES cells and differentiated cells. Given that the ES cell MVs contain components of the microtubule trafficking network, microtubule trafficking will be examined as a potential regulator of the protein content of MVs. These studies will further the understanding of MVs, a novel form of cell-to-cell communication, in the context of ES cells and differentiated cells. This will enhance our knowledge of cell- to-cell communication and provide insights that could be of great value to regenerative medicine.